Abstract

To analyze the evolution of dissolved oxygen (DO) and the nitrogen cycle inside subsurface anticyclonic mesoscale eddies (SAMEs), a coupled physical/biogeochemical model (ROMS/BioEBUS) was used to characterize the region between 20º and 40ºS and from the coast to 88ºW. For the analysis, the study region was subdivided into 8 subregions with different DO concentrations and subsurface eddies were identified for the period 2000-2008. SAMEs were characterize in the different subregions. Between 29 - 30ºS and 32 - 35ºS are the areas where most SAMEs were formed and there are three coastal regions with different properties in the water masses, whose characteristics are trapped in the structure of the eddies. The SAMEs in the north (20 - 30ºS) and center (30 - 35ºS) present in their interior a greater contribution of ESSW and the presence of denitrification processes (with a deficit of nutrients, particularly in the north) in contrast to the SAMEs in the south (35 – 38ºS) where the contribution of the SAAW increases. Anomalies observed in their cores were calculated with respect to the average conditions of each subregion. In general, the eddies move the source water from theirs formation zone creating negative DO anomalies and positive salinity respect to the surrounding waters. Furthermore, they show positive anomalies of NO3, NO2, NH4, N2O. However, the biogeochemical evolution is particular to each SAME and is mainly modulated by changes in DO concentration. Physical and biogeochemical terms that contribute to the budget oxygen during lifetime SAMEs were analyzed. In general, the terms related to horizontal oxygen advection contribute the most to the oxygen balance.